Yes, that's what it looks like. The Rio jacked up the prices for their rooms by $100 each night the Fanfest takes place. (I'm guessing if the Rio did offer a "convention discount" it would probably be whatever the original, non con weekend rate would be.)
Seriously, it would be cheaper to rent a car, take a shuttle bus or taxi from another hotel than to stay at the Rio at this point. The Rio's not a bad place to stay, but if you're just looking for someplace to just sleep and shower there are much less expensive options in Vegas.